1. The main function of an alternator is to:
(A) Convert mechanical energy into AC electrical energy
(B) Convert AC to DC
(C) Store electrical energy
(D) Step up voltage
2. The frequency of the generated EMF in an alternator depends on:
(A) Load
(B) Voltage only
(C) Speed and number of poles
(D) Rotor resistance
3. The synchronous speed of a three-phase alternator is given by:
(A) Ns = 120f/P
(B) Ns = 60f/P
(C) Ns = 2πf
(D) Ns = P/120f
4. The rotor of a synchronous machine is also called:
(A) Core
(B) Armature
(C) Stator
(D) Field
5. The stator of an alternator carries:
(A) Armature winding
(B) Field winding
(C) Exciter winding
(D) None
6. Synchronous motors run at:
(A) Constant speed
(B) Variable speed
(C) Zero speed
(D) Half synchronous speed
7. The power factor of a synchronous motor can be controlled by:
(A) Load resistance
(B) Field excitation
(C) Supply voltage
(D) Rotor speed
8. An induction motor works on the principle of:
(A) Electromagnetic induction
(B) Chemical reaction
(C) Thermal effect
(D) Magnetic hysteresis
9. The rotor of a squirrel-cage induction motor is made of:
(A) Permanent magnet
(B) Steel core only
(C) Insulated wire
(D) Aluminum or copper bars
10. The slip of a synchronous motor at steady state is:
(A) Zero
(B) Small positive
(C) Large
(D) Negative
11. The slip of an induction motor is defined as:
(A) (Ns – Nr)/Ns
(B) Nr/Ns
(C) Ns/Nr
(D) Nr – Ns
12. A three-phase induction motor is mainly used for:
(A) Driving pumps, fans, and compressors
(B) Rectification
(C) Voltage regulation
(D) Heating
13. The starting torque of a three-phase squirrel-cage induction motor is:
(A) High
(B) Low
(C) Zero
(D) Infinite
14. The rotor resistance of a slip-ring induction motor can be varied to:
(A) Control starting current and torque
(B) Control supply voltage
(C) Control speed of synchronous motor
(D) Increase losses
15. The efficiency of an induction motor is maximum at:
(A) Full load
(B) No load
(C) Half load
(D) Start
16. The main advantage of an induction motor is:
(A) Frequency variation
(B) High starting torque
(C) Field control
(D) Robust construction and low cost
17. The synchronous generator is also called:
(A) Alternator
(B) Dynamo
(C) Inverter
(D) Transformer
18. The excitation of a synchronous generator is provided by:
(A) DC supply to rotor
(B) AC supply to rotor
(C) Permanent magnets
(D) Capacitor bank
19. The power developed by an alternator depends on:
(A) Stator resistance
(B) Rotor speed only
(C) Terminal voltage, current, and power factor
(D) Supply frequency
20. The voltage regulation of an alternator is defined as:
(A) (No-load voltage – Full-load voltage)/Full-load voltage × 100
(B) Load voltage × current
(C) Terminal voltage / EMF
(D) Full-load voltage – No-load voltage
21. The EMF induced in an alternator is given by:
(A) E = IR
(B) E = 4.44 f N Φ
(C) E = VI
(D) E = P/N
22. The purpose of damper windings in a synchronous machine is:
(A) To reduce hunting
(B) Increase voltage
(C) Reduce current
(D) Store energy
23. The no-load current of an alternator is called:
(A) Stator current
(B) Load current
(C) Rotor current
(D) Excitation current
24. The main losses in an AC machine are:
(A) Stator copper, rotor copper, core, friction and windage
(B) Only copper loss
(C) Only friction
(D) Only core loss
25. The synchronous reactance of an alternator represents:
(A) Mechanical resistance
(B) Opposition to AC current flow
(C) Rotor resistance only
(D) Stator resistance only
26. The synchronous condenser is:
(A) A synchronous motor running without load to improve power factor
(B) A DC generator
(C) An induction motor
(D) A capacitor bank
27. The rotor of a synchronous motor is supplied by:
(A) Battery
(B) AC supply
(C) DC excitation
(D) Induction
28. The main disadvantage of squirrel-cage induction motor is:
(A) Low starting torque
(B) High starting current
(C) Complex construction
(D) Expensive
29. A shaded-pole induction motor is mainly used in:
(A) Fans and small appliances
(B) Transformers
(C) Alternators
(D) Generators
30. The type of rotor in an induction motor determines:
(A) Voltage
(B) Starting and running characteristics
(C) Frequency
(D) Terminal EMF
31. The speed of an induction motor decreases with:
(A) Increase in load
(B) No load
(C) Constant supply
(D) High voltage
32. The synchronous speed of a 4-pole, 50 Hz induction motor is:
(A) 1200 RPM
(B) 3000 RPM
(C) 1000 RPM
(D) 1500 RPM
33. The starting current of a star-connected induction motor is:
(A) 1/√3 of line current
(B) Equal to line current
(C) Double line current
(D) Zero
34. The starting methods of induction motors include:
(A) Only star-delta
(B) Only DOL
(C) Direct-on-line, star-delta, autotransformer
(D) Only autotransformer
35. The speed of an induction motor depends on:
(A) Supply frequency and number of poles
(B) Load only
(C) Rotor resistance only
(D) Stator voltage
36. The hysteresis loss in AC machines occurs due to:
(A) Rotor slip
(B) Resistance of winding
(C) Reversal of magnetic flux in the core
(D) Air gap
37. Eddy current loss in AC machines can be reduced by:
(A) Using thick copper bars
(B) Laminating the core
(C) Increasing voltage
(D) Increasing frequency
38. The efficiency of an alternator is maximum at:
(A) Half load
(B) No load
(C) Full load
(D) Quarter load
39. The induced EMF in a three-phase alternator is:
(A) Sinusoidal and 3-phase
(B) DC
(C) Constant
(D) Pulsating
40. The short-circuit ratio of an alternator affects:
(A) Synchronous speed
(B) Number of poles
(C) Frequency
(D) Voltage regulation
41. The rating of an AC machine is given in:
(A) kVA or kW
(B) Amperes only
(C) Volts only
(D) Ohms
42. The purpose of slip rings in a wound-rotor induction motor is:
(A) To provide external resistance
(B) To step up voltage
(C) To connect to stator
(D) To store energy
43. The main application of synchronous motors is:
(A) Transformers
(B) Heating only
(C) Lighting
(D) Power factor correction
44. The rotor of a synchronous motor must be brought near synchronous speed by:
(A) DC or auxiliary motor
(B) AC supply
(C) Capacitor
(D) None
45. A 3-phase induction motor with 6 poles on 50 Hz supply has synchronous speed:
(A) 500 RPM
(B) 1000 RPM
(C) 1500 RPM
(D) 3000 RPM
46. The mechanical power developed by a synchronous motor is proportional to:
(A) Slip
(B) Voltage only
(C) Frequency only
(D) Excitation and torque angle
47. In a generator, the frequency of generated EMF is proportional to:
(A) Rotor speed
(B) Armature resistance
(C) Load current
(D) Core material
48. The voltage induced in the stator winding depends on:
(A) Load only
(B) Rotor speed only
(C) Number of turns and flux per pole
(D) Stator resistance
49. The slip of a normal induction motor at full load is usually:
(A) 0.5
(B) 1
(C) 0.02 to 0.06
(D) Zero
50. The main difference between synchronous and induction motors is:
(A) Synchronous is cheaper
(B) Both run below synchronous speed
(C) Both run at constant speed
(D) Synchronous runs at constant speed, induction runs below synchronous speed